Attenuation of conduction delay by ischemic preconditioning reduces ischemia-induced ventricular arrhythmias

Ischemic preconditioning has been acknowledged as a powerful method of decr easing ischemic injury. However, the antiarrhythmic mechanism of ischemic p reconditioning during ischemia is unclear. We studied the effects of ischem ic preconditioning on arrhythmias and cardiac electrophysiology during isch emia in Langendorff rat hearts (n = 44). in the non-preconditioned group (P C(-); n = 24), the hearts underwent 5-min zero-flow global ischemia without any prior ischemic preconditioning. In the preconditioned group (PC(+); n = 20), the hearts were preconditioned by three cycles of 3-min zero-flow gl obal ischemia and 5-min reperfusion before undergoing 5-min global ischemia . Ischemic preconditioning reduced the incidence of ischemia-induced arrhyt hmias (PC(-): 38.9 %, PC(+); 8.3 %, p < 0.05), shortened monophasic action potential duration (MAPD, P < 0.05), attenuated conduction delay (conductio n time; PC(-): 234.2%, PC(+): 173.4%, P < 0.05) and increased the ventricul ar fibrillation threshold. Although the shortening of MAPD in PC(-) hearts was not influenced by the presence or absence of arrhythmias, conduction ti me prolongation at 3-min was more obvious in PC(-) hearts with arrhythmia t han in PC(-) hearts without arrhythmia (PC(-) with arrhythmia: 220.2%, PC(- ) without arrhythmia: 190.7 %, P < 0.05). We concluded that ischemic precon ditioning could protect the rat hearts from ischemia-induced arrhythmias an d postulated that attenuation of conduction delay during ischemia might be an important factor in the antiarrhythmic action of ischemic preconditionin g.